Synthesis of porous CuCo2O4 nanorods/reduced graphene oxide composites via a facile microwave hydrothermal method for high-performance hybrid supercapacitor applications

Electron transfer enhanced catalytic activity of nitrogen doped reduced graphene oxide supported CuCo2O4 towards the fast reduction of 4-nitrophenol in water

There has been a growing interest in the design and development of graphene based composite materials with superior performances for environmental catalytic applications. But in most of the studies the synthesis conditions require elevated temperatures and expensive working setups (high temperature furnaces, autoclaves, inert atmosphere conditions etc.). In this reported work, the nitrogen doped reduced graphene oxide supported CuCo2O4 (NG/CuCo2O4) composites were prepared through a simple one pot synthesis method under mild conditions (∼95 °C and air atmosphere) and successfully employed as catalysts for the reduction of toxic 4-nitrophenol (4NP). The characterization results revealed the successful formation of NG/CuCo2O4 composites with a possible charge transfer interaction between nitrogen doped reduced graphene oxide support of CuCo2O4. The NG/CuCo2O4 hybrids exhibited robust catalytic activity in 4NP reduction with an activity factor of 261.5 min-1 g-1. A 4NP conversion percentage which is as high as 99.5% was achieved within 11 min using the NG/CuCo2O4 catalyst. The detailed kinetic analysis confirmed the Langmuir-Hinshelwood model for the NG/CuCo2O4 catalysed 4NP reduction. The nitrogen doped reduced graphene oxide support modified the electronic levels of CuCo2O4 nanoparticles through electron transfer interactions and enhanced the catalytic activity of CuCo2O4 in NG/CuCo2O4 through improved adsorption of reactant ions and effective generation of active hydrogen species. The good reusability and stability along with profound activity of NG/CuCo2O4 catalyst makes it a promising material for wide scale catalytic applications.

Honeycomb-like biomass carbon with planted CoNi3 alloys to form hierarchical composites for high-performance supercapacitors

It is a significant challenge to combine a large pseudocapacitive material with conductive honeycomb-like carbon frameworks for long-term stable supercapacitors. Herein, hierarchical composite materials are manufactured by using biomass carbon, ZIF-67, and a mild pore former (Ni(CH₃COO)₂) to generate alloy-type CoNi₃ nanoparticles planted into conductive honeycomb-like carbon frameworks (C@ZIF-67-T). Meanwhile, the effect of carbonization temperature on the honeycomb-like pore size and the structure of composite materials is systematically investigated. As the honeycomb-like carbon skeleton structure guarantees good ionic and electronic conductivities and a large contact area, whereas the alloy nanoparticles provide a rich redox reaction for Faradaic capacitance. Therefore, the as-obtained C@ZIF-67-600 electrode presents a remarkable specific capacitance of 1044.8 F · g^-1 at 1.0 A · g^-1 and an ultra-long cycling stability with 30,000 cycles at 5.0 A · g^-1 in a three-electrode system. In addition, the assembled C@ZIF-67-600//activated carbon asymmetrical supercapacitor exhibit a high specific capacitance of 274.4F · g^-1 at 1.0 A · g^-1 and a long-term stable lifespan with a capacitance retention of 87% after 20,000 cycles at 5.0 A · g^-1. Besides, the asymmetrical supercapacitor also presents a maximum energy density of 85.13 Wh · kg^-1 at a power density of 750 W · kg^-1. Such superior electrochemical performance demonstrate that the designed electrode material provides a promising energy storage application.